Coating and method of applying the same



Sept. 28', 1937.

H. w. PARKER COATING AND METHOD OF APPLYING THE SAME Filed Jan. 11, 1936INVENTOR. Henry W. Parker BY 4 g j ATTORNEY.

A m J u M 1 U s m n. F 1 U w m 1 S N mm T U R 1AE PT Q .U M 1 H T s mDmum-uhmjznuduimmhz Patented Sept. 28, 1937 UNITED STATES 2,094,242COATING AND METsl-fsvigoF APPLYING THE Henry W. Parker, Toronto,Ontario, Canada, assignor to Rogers Radio Tubes, Limited, Toronto,Ontario, Canada, a corporation of Ontario, Canada Application January11, 1936, Serial No. 58,678

2 Claims.

My invention pertains to surface coatings and relates in particular toluminescent or fluorescent coatings and methods of applying same.

The principles involved in my improved method-may be used to producenovel, eflicient and effective coatings for many uses which will bereadily apparent, but are especially adapted to the production of anovel coating which may be rendered efliciently and effectivelyfluorescent or luminous on excitation by electrons for use in cathoderay tubes for oscillographs and for television purposes and the like.

Luminescent or fluorescent coatings for uses as above noted havehitherto been made by one of the following methods:

First, the fluorescent material is caused to adhere to the surface ofthe object being coated by a binder such as sodium silicate;

Second, the luminescent material is precipitated in powder form out ofabsolute alcohol on the surface; and

Third, the powdered luminescent material is burnt into a surface, suchas glass, by bringing the temperature of the glass up near the meltingpoint thereof.

The first of these methods has been found objectionable because thebinder which is not fluorescent prevents electrons from penetrating thebinder material sufiiciently to efiectively excite the fiuorescentmaterial. The second method is unsatisfactory because the luminescentmaterial is contaminated with carbon compoundswhichcause dimunition ofthe fluorescence due to the presence of impurities in the carboncompounds. The third method is unsatisfactory because imbedding theluminescent material in the glass causes contamination of theluminescent material and causes multiple reflection in the surface ofthe glass wall, producing a halo which destroys the definition of theimage when such surfaces are used in television.

I have discovered that if the surface to be coated is first cleaned andthen coated by a material which may be sublimated to produce on thesurface a condensation mosaic or matrix, finely powdered solid materialwill be held to the surface by electrical attraction of the material ofwhich the mosaic is made, evenly distributed and in a layer of uniformthickness, and that the material forming the mosaic may thereafter becompletelyevaporated to bring the particles of solid materialsufliciently close in contact with the surface to permit their beingheld there solely by intermolecular forces, thus producing a coatinginvolving no contamination or adulteration of the coating material andone extremely eflicient and effective.

One of the principal objects of my invention comprises the provision ofa process for producing on surfaces a. highly efilcient and effectivecoating of luminescent material.

Another object consists in the provision of a process for producing anunadulterated and uncontaminated coating which may be renderedefliciently and effectively fluorescent by electron excitation.

A further object comprises the provision of a process for coating asurface with a material which is. held to the surface effectively solelyby inter-molecular forces.

A still further object comprises producing a coating for surfaces of afinely divided material held evenly distributed over and to suchsurfaces solely by inter-molecular forces.

I accomplish all of the above noted desirable objects and features andothers which will hereinafter be apparent by the process hereinafterdescribed with respect to the drawing accompanying and forming a part ofthis specification and in which:

Fig. 1 is a partially sectioned, partially broken elevation of a form ofapparatus which may be used in carrying out my method of coating asurface such as, for example, a cathode ray tube blank;

Figs. 2, 3 and 4 show several greatly magnified views of thecondensation mosaic or matrix disposed on the surface by sublimation ofa material such as carbon disulphide; and

Fig. 5 is a curve showing the relation of interatomic forces withdistance between the coating and surface.

In order to fully disclose my novel process and product, it is deemedadvisable to describe the process as used to produce an improved articleof manufacture such as a luminescent coating for a cathode ray blank. Itis understood, of course, that such description is merely for thepurpose of explanation, as my novel process 'may be utilized for theproduction of other coated products for many other uses.

Referring now to the drawing, and especially Fig. 1, the inside of thevitreous blank l of a cathode ray tube is thoroughly washed to removeall traces of grease and other impurities and the blank is then slippedon and held in any suitable manner over the stack device which may bemade of metal or preferably glass, and which includes the tube 2provided with a flare 3, under which is disposed a container 4 holding aquantity of material such as carbon disulphide and surrounded by aheating coil 5. The tube 2 is provided at its upper extremity with adisperser plug 6 held in position as shown. The tube 2 is furthersurrounded by an additional tube 1 welded at its lower extremity to thetube 2 and provided with an outlet 8 which is attached to an aspirator(not shown).

In carrying out my process, the carbon disulphide is heated by anelectrical current which traverses the coil 5 an ignited and the fumes,because of the aspirator attached to the outlet 8, are caused to rise intube 2 where the disperser plug 6 causes them to disperse evenly overthe inner enlarged portion of the blank I. The products of combustionwhich are essentially sulphur dioxide, sulphur trioxide, some sulphur,carbon dioxide and carbon monoxide, come into contact with the innersurface of the blank i and the sulphur condenses to form a condensationmosaic or matrix on the inner surface of the blank I. The aspirator isused to suck out the excess gases and cause a draught which allows thesulphur to reach the desired part of the inside of the blank I. Theglass surface becomes milky-yellow in appearance due to the sublimationof the sulphur and the mosaic may be of varying degrees of thicknessesas shown in Figs. 2, 3 and 4 when viewed under a microscope, where Fig.2 is a microscopic view of a thin coating of sulphur, Fig. 3 is amicroscopic view of a medium thick coating, and Fig. 4 is a magnifiedview of a relatively thick coating of sulphur condensation mosaic. Themosaic is formed of minute droplets and these form on preferred centersof the surface of the glass or metal being coated. The reason for thecondensation on preferred centers is perhaps due to electrical forcesexisting between crystal inter-faces of the surface being coated. Thereasons of preferred center condensation is a surface phenomena which atpresent is not fully understood.

After the sulphur condensation mosaic has been formed, powderedluminescent material such as, synthetic willemite (crystalline zincorthosilicate with a small portion of manganese), zinc sulphide withcopper or other impurities removed, or other phosphor, as materialswhich become fluorescent when excited by electrons are now termed, isscattered evenly over the surface. The powder is prepared for evendistribution or scattering over the surface by complete drying andscreening after being reduced to powdered form. It is then stirred oragitated in order that it may be well mixed with air to give it thedesired fluff. When the powder is properly screened, dried and fluifed,it is free-flowing like a liquid due to the-mixture of air with thefinely divided material. The powder is slid down the inside of the blankand by a rapid twist of the blank the powder is evenly thrown anddistributed over the sulphur mosaic where it is held by the electricalcharge on the surface of the sulphur mosaic. The sulphur mosaic will, Ihave found, hold a uniformly thick, evenly distributed layer of thepowder as most of the excess powder slides OH, or the excess powder maybe removed by the use of any suitable wiper. Further, the excess sulphurmosaic may be removed, before the powdered material is distributedthereon, by the use of any suitable wiper to give a sharply defined edgeto the area which it is desired to coat with luminescent material. Afterthe excess luminescent material has been wiped off, the entire blank issubjected to heat to evaporate the sulphur. In this heating operationthe entire blank is heated for about twenty minutesand the sulphur iscompletely evaporated, leaving the blank free of sulphur. The heating ofthe blank serves to dispose of all of the sulphur and allows the evenlydisposed luminescent material to come into such intimate contact withthe glass surface of the blank that the material is held to the surfacesolely by inter-molecular forces. As shown in Fig. 5, theinter-molecular forces at distances of 10- cm. are negligibly small, butwhen two particles come within 10- cm. of each other they are attractedto each other by inter-molecular forces. The curve shows that this forceincreases extremely rapidly when particles come within a distance ofless than 10- cm. of each other or, in other words, approach a distancecomparable to the size of an atom.

In my experiments, I have proved that the luminescent material is heldto the surface solely by inter-molecular forces because such materialcoated by the above described process has been I analyzed and found tocontain no sulphur or other binding medium.

My method permits achieving an extremely uniform coating of luminescentmaterial of optimum thickness closely adhering to the surface of theobject being coated without being imbedded and without any contaminatingor adulterating carbon compounds or other binding material. The resultattained in the case of a luminescent screen to be rendered fluorescentby excitation of electrons is extremely effective and eflicient.

It will be obvious from the foregoing that my invention provides a novelprocess for providing improved coatings for surfaces whereby the coatingis held to the surface solely by inter-molecular forces 'to eliminatethe necessity of adulterating or contaminating binders and which, in thecase of luminescent coatings for cathode ray tubes, provides anunadulterated coating which is of optimum thickness and uniformdistribution and therefore highly efficient and effective for thepurpose intended.

Although I have shown and disclosed by way of example only oneembodiment of my invention, it will be apparent that various changes maybe made therein without departing from the intended scope and spirit ofthe invention. I do not therefore desire to limit myself to theforegoing except as may be pointed out in the appended claims in which Iclaim:

1. The method of providing a surface coating adapted to be renderedfluorescent by electron bombardment which comprises, cleaning suchsurface, exposing the surface to the products of the incompletecombustion of carbon disulphide to form a matrix of ionized sulphur onsaid surface, scattering finely powdered material adapted to be renderedfluorescent on electron bombardment on said sulphur matrix to evenlycoat said matrix with said material, removing the excess of saidfluorescent material and thereafter applying heat to said surfaceto-evaporate all of the slphur of said matrix to permit said fluorescentmaterial to adhere to said surface solely by intermolecular forces.

2. The method of providing a surface coating which comprises, cleaningsuch surface, exposing the surface to the products of the incompletecombustion of carbon disulphide to form a condensation mosaic of sulphuron said surface, scattering finely divided phosphorescent material onsaid mosaic to evenly coat said mosaic with said material, removing theexcess of finely divided material and thereafter applying heat to saidsurface to evaporate all of the sulphur forming said mosaic to permitsaid finely divided material to adhere to said surface solely byinter-molecular forces.

HENRY W. PARKER.

